1. Field of the Present Invention
The present invention relates to a transmitting apparatus that connects between networks and a method for maintaining learned information in the transmitting apparatus, and more particularly, to a transmitting apparatus and a method for maintaining learned information capable of preventing an improper deletion of the learned information due to a path failure.
2. Description of the Related Art
Conventionally, a large-scale network often has an arrangement in which each of distal networks that are directly used by end users is structured using an Ethernet™, which is easy to manage, and these networks are connected to one another using one of the asynchronous transfer mode (ATM) or the synchronous optical network/synchronous digital hierarchy (SONET/SDH), each of which assures a high speed and high reliability.
The ATM and the like has a function of autonomously detecting a failure that has occurred in a path or in a node in a network and switching the communication path to a backup path that is prepared in advance so that the point of failure can be bypassed. To utilize this function effectively and to improve the reliability of the entire network, a technique is publicly known to make it possible to detect a failure that has occurred in an Ethernet™ network using an ATM switch connected to the Ethernet™ network (see, for example, Japanese Patent Application Laid-Open No. 2004-357115).
However, even if this technique is used, when another failure has also occurred in the backup path, the communication between Ethernet™ networks is interrupted. When the communication between the Ethernet™ networks is interrupted, not only is the communication disabled during the failure period, but also some problems may occur even after the situation with the interruption has been resolved.
In an Ethernet™ network, to reduce occurrence of unnecessary traffic, a switch used for relaying packets (frames) stores therein learned information in which the receiving port of the relayed packet is shown in correspondence with the transmission source address and uses the learned information to judge the forward destinations when relaying packets. To utilize the storage area effectively, a function called aging deletes some part of the learned information that have not been used for a period of a certain length of time.
For this reason, when the interruption of the communication between Ethernet™ networks lasts longer than a certain period of time, some part of the learned information stored in the switch or the like that are related to the Ethernet™ networks experiencing the interruption will be all deleted due to the aging function. When a large amount of learned information is deleted this way, the traffic in the entire network increases by a large amount after the situation with the interruption has been resolved. In some cases, there is a possibility that a new failure occurs because of the increase in the traffic.